Compressed air regulators are necessary in compressed air applications for a number of reasons.
Your air compressor cut out pressure may be at 150 PSI or even higher. Not too many air-using applications require a compressed air supply at that pressure level. An air regulator is used to reduce the downstream air pressure from the 150 PSI (or whatever the tank pressure is) down to the desired level to operate your compressed air using application correctly.
As I noted in the video, regulators are devices that are used to change the pressure coming from the compressor receiver in all, or just part of, a downstream compressed air system, depending on where the air regulator is installed.
For example, you can have the main air regulator (the one at the compressor tank) set for 120 PSI (30 PSI less than your tank pressure) and use the 120 PSI air flow to feed the air main. Then, at each application where compressed air is to be used, you can install another air regulator to further reduce the air pressure to the right level for just that application.
The regulator will usually have an air gauge which visibly indicates the air pressure setting for the air flow to the downstream side of the regulator.
For the sake of simplicity, I have not included a gauge in the drawing above, and only showed the theoretical flow path of the regulator, to give you a sense of how they work.
The regulator acts very quickly, increasing or decreasing the flow of air through itself, so that the downstream pressure remains fairly constant. The accuracy of the air pressure downstream of the regulator is directly related to the quality of that air regulator. Lower cost regulators have a wider degree of accuracy and response time than premium and precision air regulators.
Dialing the pressure up past the supply line pressure cannot increase the downstream pressure past the tank pressure level, despite how many times you turn the knob!
Therefore, each time your air compressor cycles on it starts building pressure in the system receiver and lines again, and that sudden increase in pressure will generate a pressure-pulse in the compressed air throughout all your lines in the plant. This may be negative to your application.
Having a compressor tank or air receiver on the compressor will dampen the pressure pulse somewhat, but not entirely.
For example, let us decide that the set points on a compressor are 120 PSI on the high side, and 100 PSI on the low side. If you set the regulator to 90 PSI,, in theory that application should never see a pressure fluctuation, regardless of how many times the compressor kicks in or out. since the pulsation is occurring at the 100 PSI level, which is above the regulator setting of 90 PSI.
This pressure-pulse dampening can have benefits in terms of more consistent cycling of air cylinders, and more consistent rod speed, for example.
When this occurs, the available air pressure from the tank will continue to fall, eventually moving lower and past the regulator setting. The regulator gauge reading will reflect that pressure drop, as will the compressed air in the lines to the air using applications / air tools.
When the compressed air demand stops, air pressure will start to build, and a pressure-pulse can occur in the lines until the pressure is up past the original regulator set point.
As an energy source, compressed air one of the most expensive, since it uses other forms of energy in its generation.
Running every cylinder and every air tool at its lowest satisfactory pressure setting will save money, for sure.
For example, if you were regulating the pressure of a noxious or expensive gas, you would select a non-relieving regulator to prevent off-gassing of that poisonous gas into the plant atmosphere through the regulator, or the waste of an expensive gas through a relieving regulator.
Most industrial systems use a relieving regulator. With a relieving regulator, if the downstream pressure exceeded the pressure setting on the regulator for any reason, then the higher downstream pressure would be allowed to vent back through the regulator to the atmosphere.
Precision regulators can usually hold a line pressure within plus or minus 1/2 - 1 1/2 PSI of the set point. If you need a precision pressure setting for an application, know your pressure variation tolerance, and inform the regulator supplier, to make sure you get one that works for you. And yes, precision regulators are more expensive than general purpose regulators.
Larger pressure regulators can be air-piloted, and slaved, to smaller, remotely installed, regulators allowing pressure adjustment of a regulator in a hostile environment by one that is installed in a more benign location.
Regulators can be supplied with accessories such as locks, are supplied with or without gauges, are available in an electronic formats and in a host of configurations for specific applications.